The present invention generally relates to DC to DC regulated power supplies, and, more particularly, to improvements in such power supplies, including an active filter circuit for isolating the input power bus from reflected power changes from a variable load which exhibits a low frequency cyclical power change. The invention is especially useful in high efficiency power supplies for satellite-carried transmitters using multiple collector traveling wave tubes (TWTs) operating under widely varying modulation conditions which impose widely varying DC load requirements on the satellite power supplies. These conditions are usually encountered when a multiple collector TWT is modulated by a pulse-coded modulation with a partially filled frame and relatively slow frame rate, an example of which is time division multiple access (TDMA) modulation. At low modulation rates, the power conditioner connected between the DC input bus and the TWT appears transparent passing these power changes through to its input--namely, the satellite bus--producing an undesirable DC ripple which could effect other satellite systems.
One solution is to simply add capacitance across the collector outputs of the power supply to ground and reduce the response of the supply's regulation loop below the lowest expected frequency; however, this solution is insufficient to correct the problem because of the inherent self-regulation of the power supply which allows the current changes due to the modulation of the TWT to be reflected back into the satellite bus. The obvious answer is to place an inductor in series with the satellite bus or regulator output to form a choke-input LC filter with the added capacitance, but the weight of an inductor and capacitor, which would be effective at low frequencies, imposes a serious weight penalty.